Electrolytic hole sinking



Oct. 3, 1961 l. A. WILLIAMS 3,002,907

ELEcTRoLYTIc HOLE sINxING Filed May 20, 1959 M @-J x United States Patent Office 3,002,907 ELECTROLYTIC HOLE SINKING Lynn A. Williams, Winnetka, Ill., assignor to Anocut Engineering Company, Chicago, Ill., a corporation of Illinois Filed May 20, 1959, Ser. No. 814,450 4 Claims. (Cl. 204-143) This invention relates to methods and apparatus for the use of electrolysis in shaping of metal and metalloid materials. In my copending United States patent application Serial No. 772,960, filed November l0, 1958, for Electrolytic Shaping, kI have described and illustrated in some detail a basic method and variations thereof, together with suitable apparatus which may be used for the rapid electrolytic removal of work material. That process and apparatus are well adapted for hole Sinking and surface contouring and the present invention may be considered as an extension or improvement of the method and apparatus there set forth.

That process and the one to be here described are useful with metal work pieces which are attacked electrolytically, and with certain other conductive materials which act like metals in this respect, even though their general characteristics are non-metallic. Tungsten carbide is a nonmetallic example of this class of materials which I include in the more general term metalloid." Thus, metalloid as used herein is a generic term and refers to metals and materials which act like metals in an electrolytic organization. The term distinguishes over such electrically conductive but electrolytically inactive substances as carbon for instance.

Typically, as was explained in the referred to patent application, I advance a hollow electrode toward and into the work piece by some means while electrolyte is pumped through the hollow portion of the electrode under pressure. Various forms of electrodes may be used depending upon the character of the work, and, likewise, different schemes may be used for obtaining relative advancing movement as between the electrode and the work. As taught in that application, to promote efficient operation, the rate of ow of electrolyte should be high, the electrode to work piece spacing should be small, the current density should be high, the voltage should be low, and the temperature of the electrolyte should be relatively high (of the order of 120 to 150 F.).

Briefly, with a potential of 10 volts, or even less, current densities of the order of from l0() to 3000 amperes per square inch of effective electrode area are feasible with the process there described while still avoiding arcing between the electrode and the work. Achievement of high current at low voltages will be understood to be important when it is appreciated that the work removal rate conforms directly tothe current in the electrolytic circuit, whereas the power requirement, and hence the direct electric cost of the operation, depends upon the wattage or current times the electrical potential.

Thus. a system which requires say 2O volts to obtain a current of say 2000 amperes will have a direct operating cost for electric power about twice as high as a system which is capable of obtaining the 2000 amperes with only lO volts potential difference. This, in turn, would be bettered by a system which could obtain this current with only 5 volts potential, and so on.

It is the principal object of the present invention to provide a novel process and apparatus which is capable of electrolytically removing a greater quantity of work material and at lower electric power cost than previously used in generally similar processes.

Yet another object is to provide a novel process and apparatus which makes possible greater electrolyzing current density at a particular voltage, electrode spacing and electrolyte composition than has heretofore been possible.

Other objects and advantages will become apparent from the following description of a preferred embodiment of my invention which is illustrated in the accompanying drawings.

In the drawings:

FIG. l is a diagrammatic representation of one form of apparatus for practicing my invention; and

FIG. 2 is a similar representation of an alternative form the invention may take.

Electrolytic shaping, hole sinking for instance, depends very largely for efficient, low cost operation upon the ability to maintain high current density in the electrolyzing circuit. This promotes rapid action and, among other advantages, reduces the machine time for the operation. Additionally, it is important as previously indicated to be able to achieve high current density at low voltages, since this reduces the electric power cost` Electrolyte composition and electrode to workpiece spacing affect the resistance of the circuit, but these factors are relatively fixed in that with an optimum electrolyte and electrode, and with the work gap reduced as much as possible without danger of arcing, no further improvement can be expected from this source. As the current density is increased, the electrolyte in the work gap suffers ion depletion and becomes ineffective; also gas evolution and boiling of the electrolyte has a deleterious effect upon the operation. Elevated electrolyte temperatures are a great advantage so long as boiling is avoided. In the past this has limited practically useful temperatures to about 170 F.

By using the teachings of the present invention, much higher electrolyte operating temperatures than previously possible are easy of realization, and hence the electrical resistance is lowered. In addition, ion depletion of the electrolyte and gas and steam production within the working gap is prevented even at much higher current densities than have heretofore been thought possible. The ultimate result is to increase the usable current capacity of the system and to obtain this higher current at lower voltages.

Referring now to FIG. 1 of the drawings, a supply of electrolyte is illustrated as being contained within the reservoir 10. From this reservoir the electrolyte is withdrawn through an intake fitting 12 and supplied to a pump 14 driven by a motor 16. The pump forces the electrolyte through a riser :18 to a branched conduit 20, one branch 22 of which returns to the reservoir 10 by way of a valve 24. This bypass valve may be either automatic or manual and is adjusted to maintain a desired pressure in the conduit 20. For reasons which will become apparent presently, I prefer that this pressure be above p.s.i.g.

From the conduit 20, the electrolyte passes through a filter 26 to a heat exchanger 28 where it is heated by an electric element 30 to a predetermined temperature under the control of a thermostat 32.

The heated electrolyte then is passed through a conduit 34, valve 36, and conduit 38 to the cavity forming electrode 40. The pressure in the conduit 34, upstream of the valve 36 is sensed and indicated by a gauge 42, while a similar gauge 44 is connected to indicate the pressure in the conduit 38 which is substantially the pressure at the electrode 40. By adjustment of the valve 36, which may be an automatic pressure regulator, with possibly some adjustment of the valve 24, any desired electrolyte pressure at the electrode may be obtained during a cavity sinking operation.

The electrode 40 and the mechanism 46 for supporting and advancing the electrode may be of the type illustrated and described in my previously referred to patent appli- Patented Oct. 3, 1961 cation. The essential character of this portion of the apparatus is that a hollow electrode is mounted so as to be movable against and into the work piece 48 by any of several schemes. As the work material is removed by electrolytic action, the electrode is advanced, preferably automatically, so as to keep the gap between the end of the electrode and the work constant and quite small, of the order of a few thousandths of an inch at most.

Electrolyte is fed into the electrode and issues from the working end thereof and escapes around the electrode or through escape passages formed in the electrode, depending upon electrode design, for which see the above referred to pending application and also my copending United States patent application Serial No. 800,276, filed March 18, 1959, for Electrode for Electrolytic Hole Sinking."

With the electrolyte flowing and with the electrode advancing, a low potential high current capacity direct current circuit connected between the electrode and the work in a sense to make the electrode cathodic is energized so as to remove work material by electrolytic action.

The work 48 and the electrode supporting mechanism 46 are positioned within a tray 50 which has a drain line 52 connected to the bottom thereof leading back to the reservoir 10 shown at a somewhat lower level. Liquid electrolyte which is pumped through the electrode and escapes around the work thus falls into the tray 50 and returns to the reservoir 10.

The work area is also enclosed within a hood or housing 4, which need not be air tight but should be a conveniently close fit and should prevent splashing into the adjacent area. This hood may be made of metal with an inspection window therein, or of other suitable material which will withstand the relatively high temperatures involved. To facilitate loading, it should have an access door or panel therein, or be formed of pliable material.

As shown, the top of the hood is connected to an exhaust duct 56 leading through a motor driven blower 58 to a heat exchange chamber 60 having cooling coils 62 or the equivalent therein. These cooling coils 62 may be supplied with any suitable coolant, such as tap water for instance, so that the heat exchanger acts as a steam condenser. The outlet 64 of the heat exchange chamber 60 provides for the escape of air and for the return of condensed water to the reservoir 10. Under some conditions it may also be advisable to provide a cooling coil 66 in the reservoir 10 to reduce the temperature of the electrolyte therein slightly, if excessive evaporation of water from the electrolyte is encountered.

In practicing my method the above described system is operated as follows. The reservoir is filled with an appropriate electrolyte, the work 48 is positioned beneath the electrode 40, the pump 14 is placed in operation, and the valve 24 is adjusted to give a pressure at the gauge 42 somewhat above the desired electrode pressure. For example, the pressure may be adjusted so that gauge reads 150 p.s.i. With the valve 44 partly open so that electrolyte flows from electrode 40, the electrolyzing current is turned on and the electrode advanced toward the work until electrolytic action has proceeded sufficiently to cause the end of the electrode to be well fitted to the work, thereby producing a partial seal or highly restricted opening between the electrode and the work.

When this partial seal has been formed, the valve 44 is opened until the electrolyte pressure at the electrode is of the order of 120 p.s.i. as read upon the gauge 44. This insures rapid ow of electrolyte through the Work gap, thereby preventing ion depletion and insuring the removal of dissolved gases from the work gap before the gas saturation point is reached.

Once this high pressure, high flow rate condition has been established, the electrolyte heater 30 is energized to raise the temperature of the electrolyte well above any temperatures heretofore used, so far as I am aware,

Whereas electrolyte temperatures of 170 F. have up to now been considered to be as high as practically obtainable because of the atmospheric boiling point of water of 212 F. and because considerable heating is encountered 5 in the work gap, actually much higher temperatures can be used if the electrolyte is first pressurized in the manner described. For instance, at a pressure of 120 p.s.i., the boiling point of water is raised from 212 F. to about 350 F., and higher pressures will permit the use of even higher temperatures. Of course the dissolved salts in the electrolyte also have the effect of reducing the vapor pressure, but this effect has been ignored in the above analysis since it varies with different electrolyte composition and is not specific to a pressurized system.

As a practical matter, I prefer to use as high a pressure as is safe with the particular equipment and to use a ternperature which although extremely high by past standards is, nevertheless, safely below that at which excessive steaming takes place within the work gap. An operator quickly learns to make the appropriate adjustments to achieve this.

As soon as the hot electrolyte escapes from the Workgap it will boil until the main body of the electrolyte has cooled below the atmospheric boiling point. The steam produced is withdrawn through the duct 56 along with leakage air and is passed across the condensing coils 62. The resulting condensate ows back to the reservoir 10 while the leakage air is exhausted to the roorn or outside the building if desired. The main body of the electroylte, somewhat concentrated, is returned to the reservoir 10 by way of the line 52.

Depending upon the heat lost from the electrolyte in the pan 50, the drain line 52 and the reservoir 10, it may or may not be advisable to supply additional cooling, such as by the coil 66, in order to prevent excessive evaporation from the reservoir 10, and consequent high humidity in the building. Excessive cooling should be avoided, however, since it reduces the heat efficiency of the system and requires additional heating by the heater 30.

The arrangement illustrated in FIG. 2 is essentially similar to that of FIG l and differs thereover principally in the condensing system used. Here a motor driven pump 70 withdraws electrolyte from a reservoir 72 and supplies it hrough a conduit 74 and lter 76 to a thermostatically controlled heater 78. After filtration, the electrolyte passes through a valve 80 to the electrode 82 supported in and advanced by the fixture 84. As in the first example, there is a gauge 86 upstream of the valve 80 and a gauge 88 downstream thereof.

The fixture 84 and work 90 are positioned within a high sided pan 92 which is connected by an overow fitting 94 and drain pipe 96 to the reservoir 72. The top of the overflow fitting 94 is at such a level that the work 90 is well below the surface level of the electrolyte in the pan 92. The pump outlet conduit 74 is connected through a bypass branch conduit 98 having a valve 00 to the pan 92, so that electrolyte delivered by the pump 70 in excess of that required by the electrode 82 is bypassed to the pan 92 where it can return to the reservoir 72 by way of the line 96. To regulate electrolyte temperature, a cooling coil 102 is provided in the pan 92 while a second coil 104 may, if desired, be provided in the reservoir 72. As with the first example, the pan 92, fixture 84, and work 90 are isolated from the surrounding space by an enclosure 106.

In operation, with the pump 70 running, the bypass valve 100 and electrode pressure valve 80 are adjusted to give an electrolyte pressure at the electrode of say 120 p.s.i. after the electrode has effected a partial seal with the work. Bypassed electrolyte and that which escapes from the electrode 82 soon fills the pan 92 to the level of the outlet 94 and submerges the Work 90 and electrode 82. The electrolyte heating system 78 is energized as in the rst example so as to raise the electrolyte temperature above the atmospheric boiling point. It does not boil, however, since the pressurein the line is well above the vapor pressure even at the elevated temperature. When this superheated liquid escapes from the electrode to workpiece interface, a portion thereof flashes into steam which is quickly condensed in the body of cooler electrolyte in the pan 92. This body of electrolyte is kept cool by the electrolyte bypassed thereto from the reservoir 72 by way of the line 98 and by the direct cooling action of the heat exchange coil 102, electrolyte in the reservoir 72 being cooled as required by the coil 104. Gases formed by the electrolytic action escape through leaks around the enclosure 106, or may be removed therefrom by a duct or vent especially provided for the purpose. y A

A common combination of inventive features, among others, of both these examples is that, in the systems, the electrolyte is used at the electrode at high pressure, the electrolyte is heated above the atmospheric safe temperature after it has been pressurized, and there are facilities for handling the steam which forms as soon as the electrolyte escapes from the electrode to workpiece interface. The overall result of this is that higher current densities can be used, since gas and steam formation and ion depletion in the working gap become less of a problem, because of the high electrolyte pressure which increases gas solubility and the high flow rate which rapidly renews the working electrolyte. Furthermore, this high current density can be achieved with lower voltages, since the much higher electrolyte temperature results in higher chemical activity and hence lower electrical resistance. As previously explained, the higher current density which is possible and the lower voltages which are necessary to produce these currents have a markedly beneficial elfect upon the cost of operation.

From the above description of my invention as eX- emplied in the embodiments illustrated, it will be apparent that variations in the method and apparatus may be made without departing from the scope or spirit of the invention. The scope of the invention, therefore, is to be determined by the scope of the following claims.

Having described my invention, what I claim as new and useful and desire to secure by Letters 'Patent is:

1. The` improved method of removing work material by electrolytic action at the interface between a workpiece and the working face of a cathodic electrode in the presence of an electrolyte, which comprises supplying the electrolyte at a pressure of several atmospheres to the interface for ow therethrough, maintaining the electrolyte under substantial pressure while the electrolyte is within the interface, and heating the electrolyte after itr has been pressurized but before it leaves the interface to a temperature above the electrolyte atmospheric boiling point but below the electrolyte boiling point at the interface pressure, whereby steaming of the electrolyte within the interface is substantially eliminated but takes place immediately after the electrolyte escapes from the interface.

2. The improved method of removing work material by electrolytic action at the interface between a Workpiece and the working face of a cathodic electrode in the presence of an electrolyte, which comprises providing a reservoir of electrolyte at substantially atmospheric pressure and at a temperature below the electrolyte atmospheric boiling point, continuously removing electrolyte from the reservoir and raising the pressure thereon to several atmospheres and supplying the pressurized electrolyte to the interface for ow therethrough, maintaining the electrolyte under substantial pressure while the electrolyte is within the interface, and heating the electrolyte after it has been pressurized but before it leaves the interfaceV to a temperature above the electrolyte atmospheric boiling point but below the electrolyte boiling point at the interface pressure, whereby steaming of the electrolyte within the interface is substantially eliminated but takesplaceimrnediately after the electrolyte escapes from the interface.

3. The improved method of removing work material by electrolytic action at the interface between a workpiece and the working face of a cathodic electrode in the presence of an electrolyte, which comprises providing a n reservoir of electrolyte at low pressure and at a temperature below the electrolyte boiling point at said low pressure, continuously removing electrolyte from the reservoir and raising the pressure thereon to a level well above said low pressure and supplying the pressurized electrolyte to the interface for llow therethrough, positioning the electrode within a few thousandths of an inch of the workpiece to produce a high order of restriction to the ow of electrolyte through Ithe interface to maintain the electrolyte under pressure until it escapes from the interface, heating the electrolyte after it has been pressurized but before it escapes from the interface to a temperature above the said electrolyte low pressure boiling point but below the electroylte boiling point at the interface pressure, removing dissolved gases and steam from the'electrolyte as i-t escapes from the interface, condensing the steam, and returning the deaerated electrolyte including the condensed steam to the reservoir.

- 4. In an apparatus for the electrolytic removal of work material the combina-tion comprising an electrode having a passage for the liow of electrolyte therethrough, means for supporting said electrode and a workpiece in opposition to said electrode, means for maintaining a work gap between the electrode and the workpiece of no more than a few thousandths of an inch so as to restrict the flow of electrolyte through said work gap, means forming a low pressure reservoirv for electrolyte, pumping means connected for removing electrolyte from said reser` voir and for supplying electrolyte to said electrode at an elevated pressure for flow through said electrode, heating means connected for heating the electrolyte ata position between said pumping means and said electrode, means for collecting electrolyte escaping from said electrode and for returning the escaped electrolyte to said reservoir, and means for controlling the temperature of the electrolyte in said reservoir.

References Cited in the file of this patent UNITED STATES PATENTS Dedication 3,002,907.Lynn A. Williams, \Vnnetka, Ill. ELECTROLYTIC HOLE SINKING. Patent dated Oct. 3, 1961. Dedication led Deo. 23, 1971, by the assignee, Anocut Engineering Company. Hereby dedoates to the Publio the portion of the term of the patent subsequent to Dec. 24, 1971.

[Oficial Gazette March 14, 1972.]

Dedication 3,002,907.-Lynn A. Williams, Wnnetka, Ill. ELECTRQLYTIO HOLE SIN KING. Patent dated Oct. 3, 1961. Dedication filed Deo. 23, 1971,

by the assignee, Anocnt Engineering Company. Hereby dedcates to the Public the portion of the term of the patent subsequent to Dec. 24, 1971.

[Oycz'al Gazette March 14, 1.972.]

Dedication 3,002,907.-Lg/nn A. Williams, Vnnetka, Ill. ELECTROLYTIC HOLE SINKING. Patent dated Oct. 3, 1961. Dedication led Dec. 23, 1971, by the assignee, Anmut Engineering Uompcmy. Hereby dedcates to the Public the portion of the term of the patent subsequent to Dee. 24, 1971.

[Oficial Gazette March Il, 1.972.] 

1. THE IMPROVED METHOD OF REMOVING WORK MATERIAL BY ELECTROLYTIC ACTION AT THE INTERFACE BETWEEN A WORKPIECE AND THE WORKING FACE OF A CATHODIC ELECTRODE IN THE PRESENCE OF AN ELECTROLYTE, WHICH COMPRISES SUPPLYING THE ELECTROLYTE AT A PRESSURE OF SEVERAL ATMOSPHERES TO THE INTERFACE FOR FLOW THERETHROUGH, MAINTAINING THE ELECTROLYTE UNDER SUBSTANTIAL PRESSURE WHILE THE ELECTROLYTE IS WITHIN THE INTERFACE, AND HEATING THE ELECTROLYTE AFTER IT HAS BEEN PRESSURIZED BUT BEFORE IT LEAVES THE INTERFACE TO A TEMPERATURE ABOVE THE ELECTROLYTE ATMOSPHERIC BOILING POINT BUT BELOW THE ELECTROLYTE BOILING POINT AT THE INTERFACE PRESSURE, WHEREBY STEAMING OF THE ELECTROLYTE WITHIN THE INTERFACE IS SUBSTANTIALLY ELIMINATED BUT TAKES PLACE IMMEDIATELY AFTER THE ELECTROLYTE ESCAPES FROM THE INTERFACE. 